DC-DC converters are devices that receive a DC voltage and output a DC voltage of another size by transforming the same, and are widely used in various fields. DC-DC converters are classified into a buck converter operating by a voltage source and outputting a voltage lower than an input voltage, a boost converter operating by a current source and outputting a voltage higher than an input voltage, and a buck-boost converter wherein a buck converter and a boost converter are integrated and are capable of stepping up and down an input DC voltage. Among them, a buck-boost converter is widely used in various fields as the buck-boost converter is capable of stepping up and down an input DC voltage, and thus an input voltage range may be wide and high efficiency is realized within the entire range of the input voltage.
For such a buck-boost converter, in a small power grid of less than 1 MW of a rated power lower than the micro grid, research on the application of a switching mode power supply (SMPS) of a DC nano grid is actively being studied.
In other words, in a conventional DC nano grid system, a bi-directional converter of an energy storage device may adjust amount of charging and discharging of a battery and control a DC bus voltage when a black out occurs or system failure occurs.
However, an isolated buck-boost converter may be useful since an input and an output are isolated, but usage of the transformer should be limited as primary energy of the transformer is output to secondary output when a switch is ON or OFF. In addition, in case of non isolated buck-boost converter, since input ripple current is large, a filter circuit is required in an input of the converter. In addition, a small circuit configuration where input ripple current is small is also required, and the structure is very complicated due to the necessity of additional components compared with the basic circuit configuration.
When a control device for such a buck-boost converter operates from no load to full load, and a gain is set to be higher than a predetermined reference value to improve a response speed of switching control, a transient state occurs largely. However, when the gain is set to be low to prevent such a situation, the response speed of the switching control becomes slow.
Accordingly, the present applicant proposes a buck-boost converter having a simple structure and being capable of stepping up and down an input voltage having a wide range, improving the entire power efficiency by reducing a number of switching elements, minimizing switching loss and reducing conduction loss, and by using a control module improving a response speed of switching control of the buck-boost converter, and a control device for the same.